Emoncms low write mode - 1S interval data

i used emoncms a few years ago, now i wanted to use it again on an ubuntu PC with ssd, i need to send values every second, i see that isnt possible now, is any way to deactivate the low write mode in emoncms?.


Low Write mode is a mechanism whereby readings are written to RAM first then written to storage by default every 300s. This was primarily to extend the life of the SD Card.

I think the minimum emoncms will process inputs is every 5s. This is independent of the ‘Low Write’ mechanism. I’m not sure it has ever been more frequent.

Hello borpin,
I remember i have use emoncms in 2014 and i have Made Tests with it , i got 100 ms feeds :-), i am using IT sending values from a PLC (S7 1200) and logging the values in emoncms.
Its posible to Hack emoncms to get IT to Store feeds with 1 Second Intervall?.

I wasn’t aware of a limit (other than a practical one) when using your own emonCMS. I had problems with the 12-input emonTx4 sending its data in two consecutive packets as two different nodes, this requires a delay between packets or the second fails, but this delay is IIRC 120 ms or so (and I seem to remember Trystan has tweaked the emonPi to improve things). It’s probably related to how long it takes the emonPi front end to recognise it’s got a radio packet and empty the buffer in the RFM69CW. If it’s receiving data directly by serial, USB, Ethernet or Wi-Fi, the rules will be different.

However, emoncms.org is rate-limited to one packet of data every 10 s.

99% sure the input process offers 5s, 10s as the option for the timeseries Feeds.


That’s Trystan’s view of useful and practical values for the Fixed Interval TimeSeries. not a limitation of emonCMS. I think this could be changed for a custom version, or (at the cost of file size) the Variable Interval TimeSeries should go quite a bit faster.

As written and distributed it is!

Thats clear, and emoncms was made for other purpose as i need it, If its not possible to change the Intervall to 1 sekond in new distribution, ITs possible to Install in an Ubuntu Maschine the old emoncms? I believe IT was V8.4, how can i do that?.
I need the values in the feeds as they come from the PLC, i dont need average values.

I really Like this project and want to use emoncms, its any posibility to Install an old version to have faster Intervals?, or know someone a Hack i can do to do IT with the newest emoncms?


I found a way, i send the http request with an Unix timestamp , that worked , now i See Datapoints at 1 Second intervals, thats enough for me, i believe i cant do IT faster because the Unix time used has 1 second resolution.

1 Like

I am testing, i see the feeds storing at 1 s interval, but after a while the feeds are stored with an interval from 10 seconds, i believe i can only see data with 1 second interval if the data is in ram stored, when is stored in ssd it changes to 10 seconds, its that right?.

Which type of database are you using, Fixed Interval or Variable Interval?

Fixed Interval has the start time and interval set and stored as metadata when the Feed is created. If you have used 10 s because this is the minimum emonCMS can accept without being customised for your application, then only the last data that arrives in each 10 seconds long ‘slot’ will be stored.

Variable Interval stores the data and the time it arrives in a record in the database. Therefore Variable Interval is the database you should be using.

The advantage of Fixed Interval is the size of the database grows at approximately half the rate of Variable Interval, because it stores only the data, compared to data plus time for the Variable Interval database.

This is my understanding of how emonCMS works.

Hello Robert,
I am using both Database, i am sending every Second a number that i am adding 1 every Second, the Feed with variable Intervall IS showing every Second a number , but after a few minutes the Same time lapse has only a value every 10 Seconds, you know maybe any Hack i can do to change that?, i want to Store every Second the value.
Or maybe IS possible to Install an old emoncms in Ubuntu, but i dont know how.
Or maybe someone knows another Project i can use that Stores values in faster Intervals?

For me is working all nice when the data is in the redis buffer, the intervall is 1 second in the csv output and in the Graph, when the buffer is writed my intervals change to 10 seconds, its possible to write the buffer with 1 second intervall?, where i can find that setting?.

I’m afraid I do not know how Redis works, so I cannot help you. You need someone who knows more about emonCMS than I do.

@borpin or @TrystanLea Can either of you help here?

IT Looks Like isnt possible, have to Look for Other way to Log my variables.

Grafana? I know nothing about it, but others have used it with OEM equipment.

Emoncms was easy to implement and has nice graphs, i Like this Projekt, thats why i tried to use it, i will Look at grafana, maybe It will fit better for me, thanks Robert.

Hello @Solrac76 here’s the hardcoded 5s minimum interval in PHPFina:

also limited to 10s when creating feeds here: https://github.com/emoncms/emoncms/blob/master/Lib/enum.php#L81

Hello @TrystanLea ,
i have made the changes, i see the 1 second interval with the right values when i download the Feed CSV, but in Graph it shows me only 10 seconds intervals with value when i hover the mouse over the value line and in multigraph i cant zoom to much, if i zoom more to see under 30 sec. the value line disapears.
Thanks for your help.